The crowd listen to leader of the Labour Party Jeremy Corbyn as he delivers a speech at a campaign rally in Beaumont Park after launching the Labour Party Election Manifesto in Huddersfield, England | Leon Neal/Getty Images

Britain's Shadow Chancellor John McDonnell on Friday said Jeremy Corbyn’s most influential union backer, Len McCluskey, "woke up more optimistic" a day after he told POLITICO that 200 seats for Labour in the general election would be a success.

McCluskey, the general secretary of the U.K.’s biggest trade union Unite, said in an interview published Wednesday that Labour will have had a “successful campaign” if it manages to win just 200 of the 650 House of Commons seats.

McCluskey later walked back from the remarks, saying he was "now full of optimism. If I was having that interview now I would not be making those comments."

When asked about Unite chief's comments on BBC Radio 4, McDonnell said McCluskey "just woke up the next morning a bit more optimistic."

The shadow chancellor said he was convinced Labour would come away victorious after next month's snap election "on the basis of [a message of] positive hope."

"We’re going to win. We’re rising in the polls and now that people have seen this Tory manifesto … people are going to be angry."